Sound waves(The behavior of soundboards)

John Delacour JD@Pianomaker.co.uk
Tue, 18 Dec 2001 18:56:03 +0000


At 8:00 AM -0600 12/18/01, Ron Nossaman wrote:

>So you never said the bridge didn't move. Quite true, you didn't. You said
>it didn't have to move to make quite satisfactory piano sounds,

I said that the sound was impaired.  You said that the sound ought to 
be completely killed, as it would be according to your theory.

>  but aren't interested in  actually trying it to prove your 
>intuition - even to
>yourself. Meanwhile, the unchallenged fact that the bridge does move has
>little or nothing to do with sound production, but it's definitely not the
>string movement that is moving the bridge.

What I have suggested all along is that the vibrations travel from 
the string thtough the bridge to the soundboard.  The soundboard 
responds with vibrations in the vertical plane and that it is these 
movements that cause the bridge to move up andf down.  That is the 
whole tenor of my proposition, which neither you no Del seem to have 
noticed.  Your proposition is the soundboard moves because the bridge 
is moved.

>  The rest seems to be details revolving around this core premise, 
>unless I've missed some major connection. I've got to agree with you 
>on one point at least. My ignorance is certainly getting in the way 
>of me seeing the sense and usefulness of this line of thinking.

I'm not begging for any agreement, so you can save yourself the effort.


I now string one note only of my piano with two strings, tune them to 
the same pitch and strike them with a hammer in such a way that while 
one of the strings is tending to move the bridge upwards the other is 
tending to move the bridge downwards.  You say that this will be 
impossible and unprovable, and I answer that this state of affairs is 
likely to exist in any case for a proportion of the time the note is 
sustained, so in fact I do not have to strike the strings in any 
special way.  The more often I hit the two strings, the more often I 
will be able to observe a situation where the upward force of the 
vibration in one string is exactly counterbalanced by the downward 
force of that in the other.  Under these conditions the bridge cannot 
be moved by the strings, since a body only moves in reaction to a 
force and in these circumstances there is a zero force acting on the 
bridge.

It would be better of course to emulate the vibrations of the strings 
by some electical device that could consistently produce the two sets 
of "opposite-phase" mutually cancelling vibrations.

I say that the sound emitted from the soundboard will be practically 
identical whether the two strings (according to your theories) are 
acting in concert to move the soundboard in one direction or whether 
they are counteracting each other and therefore quite unable to 
produce any movement.

Answer me that.

JD








This PTG archive page provided courtesy of Moy Piano Service, LLC